In recent thin film transistor substrates which comprise liquid crystal display panels, as a switching element for each sub-pixel, which is a minimum unit of an image, a thin film transistor (hereinafter also referred to as a “TFT”) using a semiconductor layer made of an oxide semiconductor (hereinafter also referred to as an “oxide semiconductor layer”) and having favorable characteristics of high mobility, high reliability, and low off-state current have been proposed as a replacement of a conventional TFT using a semiconductor layer made of amorphous silicon.
For example, Patent Document 1 discloses a TFT which includes a gate electrode provided on a substrate, a gate insulating film provided to cover the gate electrode, an oxide semiconductor layer provided on the gate insulating film so as to overlap the gate electrode, and having a channel region, a source region, and a drain region, a titanium layer provided on the source region and the drain region of the oxide semiconductor layer, a source electrode and a drain electrode which are made of copper and respectively connected to the source region and the drain region of the oxide semiconductor layer, with the titanium layer interposed therebetween, wherein a contact resistance between the oxide semiconductor layer, and the source electrode and the drain electrode, is reduced by the titanium layer disposed between the oxide semiconductor layer, and the source electrode and the drain electrode.